Error: Unknown 'stores' extension 'mongo'

[Roshanthan]

i have followed the tutorial and installed cubes it worked fine until i tried to use mongo as backend. I am getting the following error: Unknown 'stores' extension 'mongo'

i have used for installation:
pip install cubes[all]
git clone git://github.com/DataBrewery/cubes.git
cd cubes
pip install -r requirements.txt
pip install -r requirements-optional.txt
python setup.py install

my slicer.ini:
[store]
type: mongo
url: mongodb://localhost:27017/
database: windesheimCube
collection: windesheimCube
model: mongo_model.json

[workspace]
log_level: info

[server]
host: localhost
port: 5000
reload: yes
prettyprint: yes
allow_cors_origin: *

Is this an issue with cubes or am i doing something wrong?